On the Effect of Recycling of Kraft Paper on Selected Fines Properties, 1997 Recycling Symposium Proceedings

Fines may play an important role in strength development during consolidation of a paper sheet, depending on the amount of fines, their bonding capacity, and the stiffness of the pulp fibres. Recycled chemical pulps are of special interest because recycling affects both the bonding capacity of the fines and the fibre stiffness. Fines and fibres lose some of their swelling potential during recycling. The purpose of this study was to investigate the effect of controlled recycling of chemical pulp on selected fines properties. The secondary fines from virgin pulp, and the primary and secondary fines from recycled pulp were characterised according to swelling ability, turbidity, sedimentation volume, number of acidic groups, surface charge, and chemical composition. The effect of secondary, primary recycled and secondary recycled fines on some pulp and paper properties were also measured. Results showed that secondary fines from the virgin pulp were more swollen than fines in the recycled pulp, and that secondary recycled fines were more swollen compared with primary recycled fines. Sedimentation volume and turbidity measurements indicated that primary recycled fines particles were smaller in size compared with both the secondary and secondary recycled fines. It was also found that primary recycled fines had a higher acidic group content compared with secondary recycled fines, but less than the secondary tines. Only minor changes occurred in chemical composition, but secondary recycled fines seemed to be more like the long fibre fraction in composition compared with the other types of fines. It is proposed that at least part of the primary recycled fines were originally secondary fines and external fibrils in the virgin pulp, and that these fines and fibrils are damaged during disintegration of the recycled paper. Thus smaller particles are created compared with the secondary fines.